1. Field of the Invention
The present invention relates to a fuel cutoff valve that is attached to the top of a fuel tank and opens and shuts off a connection conduit for connecting inside of the fuel tank with outside to connect and disconnect the inside of the fuel tank to and from the outside.
2. Description of the Related Art
A known fuel cutoff valve as disclosed in JP No. 2000-130271A has the structure shown in FIG. 18. FIG. 18 is a sectional view showing a fuel cutoff valve 100 attached to the top of a fuel tank. The fuel cutoff valve 100 includes a casing body 110 that has a valve chest 110S for connecting inside of the fuel tank with outside, a float 120 that is received in the valve chest 110S and moves up and down according to the fluid level in the fuel tank, a spring 122 that is located above the float 120, a first valve disc 124 that is mounted on the top end of the spring 122, and a second valve disc 126 that is located on the center of the float 120.
In the fuel cutoff valve 100 of the above structure, when the fuel level in the fuel tank reaches a preset first fluid level by the supply of fuel, the float 120 moves up and causes the first valve disc 124 to shut off a first connection conduit 112b. When the fuel level further rises to a preset second fluid level, which is higher than the preset first fluid level, the second valve disc 126 shuts off a second connection conduit 131a against the pressing force of the spring 122. The second connection conduit 131a has a narrower passage area than the first connection conduit 112b. Namely the passage area is narrowed in two stages according to the fuel level. This does not seal the fuel tank abruptly and prevents a blowing back flow of the fuel at a filler neck.
In the prior art fuel cutoff valve 100, the preset second fluid level that causes the second valve disc 126 to shut off the second connection conduit 131a is specified by the load of the spring 122. Significant labor and time are thus required for setting the load of the spring 122 and its regulation.